From Sega Retro

Sega Game Toshokan (セガゲーム図書館), meaning Sega Game Library, is a Sega Mega Drive cartridge distributed with select Mega Modems starting 1991. With the Mega Modem connected, this cartridge in the cartridge slot, and a Sega Meganet subscription, consumers could download and play select Mega Drive games exclusively available through the service, all of which came out on the service in 1991.

Two such games, Flicky and Shi no Meikyuu: Labyrinth of Death (called Fatal Labyrinth overseas), saw retail release outside Japan prior to the launch. Another, Teddy Boy Blues, was a port of an earlier game that had already been released internationally. A fourth, Columns, was already released in Japan retail. All the others were never released outside Japan and originated on Game Toshokan. All the games were eventually rereleased as part of the Game no Kanzume series, several Sega Ages compilations, and Sega's B-Club! service for downloading Mega Drive games to play on a PC.

The paid service ended in September 1992, possibly continuing for existing subscribers or as a free service until March 1993. It was said to have had 3,500 subscribers at the time that the service was announced to end.[1]